The development of power electronic devices with improved performance, increased reliability, compact size, and reduced weight requires the passive components to be embedded within a printed wire board (PWB). This technology could free up surface space, increase device reliability, and minimize electromagnetic interference and inductance loss. The capacitance density of a dielectric is proportional to its permittivity or dielectric constant divided by the thickness of the dielectric material. A high capacitance density capacitor can be fabricated by using thin film dielectric of high permittivity. High permittivity (high-K) materials include perovskite ceramics of general formula ABO3, such as crystalline lead zirconate titanate [Pb(Zr,Ti)O3, PZT], lead lanthanum zirconate titanate [(Pb,La)(Zr,Ti)O3, PLZT], lead magnesium niobate [Pb(Mg1/3Nb2/3)O3, PMN], barium titanate (BaTiO3, BT), and barium strontium titanate [(Ba,Sr)TiO3, BST]. Thin ceramic films may be deposited on base metal foils, such as nickel and copper. Base metal foils are subject to undesirable oxidation and require low oxygen partial pressures during high temperature annealing for formation of the desired crystalline phase of the ceramic that exhibits high-K. The low oxygen partial pressures, however, can result in complications such as high dielectric losses due to reduction of dielectric materials, suppression of dielectric constant due to reactions between the thin film dielectrics and the substrates of metal foils. Therefore, finding an effective method for the fabrication of high-K dielectric films on metal foils has been a hot research area [1-3]. Zou et al. [1] describe a method of using LaNiO3 (LNO) buffer on a nickel substrate to prevent oxidation at the interface and therefore enable high temperature annealing processes in air. Copper is a preferred substrate due to its ready availability and PWB processing compatibility. Borland et al. [2] describe a method of producing BST films on Cu substrates by chemical solution deposition; and indicate that a suitable oxygen partial pressure of about 10−10 atm must be maintained during the high temperature annealing. Maria et al. [3] describe a method of controlling the oxygen partial pressure during high temperature annealing by using gas mixtures between CO and CO2 or H2 and H2O, in which the thermodynamic properties of the oxygen-containing substance are used to achieve the desired oxygen partial pressure (pO2) during the high temperature annealing.
Recently, (Pb,La)(Zr,Ti)O3 (PLZT) and Pb(Zr,Ti)O3 (PZT) based perovskite materials deposited directly on copper metal foils have been of great interest because of reduced manufacturing costs achievable by replacing expensive noble metal electrodes in embedded capacitor applications. Traditionally, lead-based perovskite materials have been deposited on expensive Pt/Si substrates by sol-gel synthesis and crystallized at high temperatures in air. The in-air processing capability cannot be extended to perovskites deposited onto copper substrates, because the ease with which copper forms a copper oxide (Cu2O) layer under such processing conditions. The low-permittivity and linear dielectric Cu2O layer degrades the ferroelectric properties of the resultant capacitor structures. Kingon et al. [4] reported that a strict control of the oxygen partial pressure (pO2) within the thermodynamic processing window (pO2 of about 10−13-10−17 atm) during crystallization is necessary to avoid the formation of copper oxide, while maintaining the high quality and phase integrity of the perovskite material. Losego et al. [5] indicate that careful choice of solution chemistry is important to avoid copper oxidation and micro-cracking in films made directly on copper substrates. While acetic acid [4-7], alkanolamine [6], and acetylacetone [6], based chelation methods have been used in the literature to deposit films on copper, 2-methoxyethanol (2-MOE)-based chemistry has been reported to promote the desired reactions and can solubilize a variety of different precursors [8].